The present invention relates to a sealing member and a sealing structure provided in a valve installed, e.g., in a pressure vessel or a fluid flow path filled with fluid under a high pressure.
Gas tanks filled under a high pressure (high degree of compression) with hydrogen gas or natural gas as a fuel gas are carried on natural gas vehicles or fuel cell vehicles. For example, the filling amount of hydrogen gas of 35 MPa and 70 MPa is discussed within a framework of regulations relating to hydrogen gas supply stations and high-pressure hydrogen vessels based on high-pressure gas safety rules that have been studied in the governmental agencies. There are a variety of gas tanks filled with such high-pressure gases, e.g., metal or plastic tanks, but in the field of vehicles, pressure vessels made from a fiber-reinforced plastic (FRP) in which a liner is covered with an outer shell of a FRP are mainly used due to high strength and small weight thereof.
Valves for blocking the flow of fluid, which are called shut valves, are typically installed in intake and release openings for fluid in the pressure vessels for storing and discharging various high-pressure fluids (liquids, gases) in various applications including the above-mentioned automotive applications. Furthermore, a sealing structure having a sealing member is usually provided in the valve to ensure reliable sealing of the fluid. As an example of such a sealing structure, a structure for sealing a sleeve (mouthpiece) where a valve is installed by using an elastic sealing member such as an O ring is disclosed in Japanese Patent Application Laid-open No. 11-13995. Sealing structures using such O rings are widely used in the valves themselves. Furthermore, structures using angular rings rather than O rings and structures in which a rubber material serving as an elastic substance (material) is joined with the valve by vulcanization molding are also known.
However, if the pressure in the pressure vessel is increased, for example, to the above-mentioned 35 MPa or 70 MPa, the difference in pressure between the spaces that have to be separated and sealed with a valve becomes extremely high. As a result, in a sealing structure using the conventional sealing member such as an O ring, the sealing member is deformed by the difference in pressure and sometimes there is a risk of the sealing member being pushed out from the groove into which it was fit. Therefore, sufficient sealing performance cannot be achieved. Furthermore, in structures in which a rubber material is joined to a valve by vulcanization valve, the deformation caused by the aforementioned difference in pressure is also significant and a sufficient sealing performance cannot be attained.
In the latter case, a groove where the rubber material is vulcanized and joined can be made very shallow and a very thin rubber material can be used with the object of inhibiting the deformation of the rubber material. However, in order to conduct the vulcanization molding, a groove depth above a certain fixed value has to be ensured. Furthermore, increasing the hardness of the rubber material can be considered as means for improving resistance to deformation. However, rubbers with a certain high hardness tend to be difficult to unit each other by vulcanization molding. According to the information known to the inventors, if the difference in pressure between the spaces that have to be sealed with a valve exceeds approximately 20 MPa (or approximately several MPa for some valve sealing materials and structures), the required sufficient sealing performance is difficult to achieve and hermeticity of vessels is difficult to maintain with the above-described conventional sealing structures. Furthermore, the same problem is associated not only with the pressure vessels, but also with shut valves in fluid flow paths where a large pressure difference is generated between the spaces that have to be sealed.
The present invention has been made in view of the above circumstances and has for its object to provide a sealing member in which a sufficient sealing can be attained even when the difference in pressure between the spaces that have to be sealed with a valve exceeds several tens of MPa (or several MPa).